File: closest_point.h

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// Copyright 2009-2021 Intel Corporation
// SPDX-License-Identifier: Apache-2.0

#pragma once

#include "../math/vec.h"

namespace embree
{
  Vec3fa closestPointTriangle(Vec3fa const& p, Vec3fa const& a, Vec3fa const& b, Vec3fa const& c)
  {
    const Vec3fa ab = b - a;
    const Vec3fa ac = c - a;
    const Vec3fa ap = p - a;

    const float d1 = dot(ab, ap);
    const float d2 = dot(ac, ap);
    if (d1 <= 0.f && d2 <= 0.f) return a;

    const Vec3fa bp = p - b;
    const float d3 = dot(ab, bp);
    const float d4 = dot(ac, bp);
    if (d3 >= 0.f && d4 <= d3) return b;

    const Vec3fa cp = p - c;
    const float d5 = dot(ab, cp);
    const float d6 = dot(ac, cp);
    if (d6 >= 0.f && d5 <= d6) return c;

    const float vc = d1 * d4 - d3 * d2;
    if (vc <= 0.f && d1 >= 0.f && d3 <= 0.f)
    {
        const float v = d1 / (d1 - d3);
        return a + v * ab;
    }
    
    const float vb = d5 * d2 - d1 * d6;
    if (vb <= 0.f && d2 >= 0.f && d6 <= 0.f)
    {
        const float v = d2 / (d2 - d6);
        return a + v * ac;
    }
    
    const float va = d3 * d6 - d5 * d4;
    if (va <= 0.f && (d4 - d3) >= 0.f && (d5 - d6) >= 0.f)
    {
        const float v = (d4 - d3) / ((d4 - d3) + (d5 - d6));
        return b + v * (c - b);
    }

    const float denom = 1.f / (va + vb + vc);
    const float v = vb * denom;
    const float w = vc * denom;
    return a + v * ab + w * ac;
  }
}